For OEM systems (Dell/HP/Lenovo/Gateway/Acer/etc etc) I only assume that the motherboard will be compatible with the short list of CPUs that were originally available for configurations of a particular model/year, and those choices rarely include K-series CPUs. ie, if CPU choices for a given system were: i3-6100, i5-6500, i7-6700, then that's all I'd assume is compatible.
That's what Wolf is trying to get info for. If we know the brand and model (ie Dell Optiplex 990) then we can look up the system configurations that were available.
Having the model # of the mobo may be helpful to determine [via google] what system it came out of, so then we can look up what CPU configs that system had. But most of the time (unlike aftermarket mobos which each have a dedicated webpage laying out CPU compatibility, BIOS updates, etc etc) there's little/no documentation that tells you what CPUs are compatible with OEM mobos.